At least since 1971, optical probes have been produced conventionally and have been introduced into the diphasic medium to be measured and whose functioning mainly depends on the presence of optical fibers, the extremity of these fibers being suitably machined so as to provide good vision.
Such optical fibers function as follows: if light is sent by means of such a fiber, this light is refracted inside the medium if the sensitive extremity of the fiber is surrounded with liquid and, on the other hand, this light is totally refracted and accordingly returned into the same fiber when the sensitive extremity is surrounded with gas or vapor. Consequently, if the reflected light returned into the emitting fiber is detected, this implies the existence of a gaseous phase around the sensitive extremity of this fiber.
Such a known device accordingly makes it possible to know at each moment whether at any particular point of a medium this device is present in a liquid phase or a gaseous phase. However, a single fiber is unable to obtain information concerning the direction and speed of a possible flow inside this diphasic emulsion.
In order to resolve this problem, the invention aims to provide a double optical probe or biprobe comprising side by side two parallel optical fibers, as shown in FIG. 1. Such an optical probe mainly comprises a hollow cylindrical tube 2 made of a rigid material and intended to penetrate as far as the emulsion point it is desired to observe. This hollow cylindrical tube 2 is blocked off at its observation extremity by a cylindrical support 4 comprising two orifices, guiding tubes 6 and 8 being mounted into these orifices and intended for passage of two optical fibers 10 and 12 whose extremities 14 and 16 have been suitably machined so as to allow for correct optical observation. The unit of the system, that is the hollow cylindrical tube 2, rotates around its longitudinal axis XY. One can readily understand that such a known device is able to detect and even measure a flow speed of the observed biphasic medium as soon as the liquid particles and/or gas bubbles were to move successively in front of the extremities 14 and 16 of the optical fibers 10 and 12. By measuring the transit time of such phenomena between the two extremities 14 and 16, it is relatively simple to accurately deduce the flow speed of the diphasic emulsion at this location.
Nevertheless, it can be readily understood that the optical biprobe of FIG. 1 is able to only measure a speed vector contained in a plane perpendicular to its axis XY. This accordingly considerably limits the application and requires several successive penetrations of this biprobe along two different directions if it is desired to disclose and measure the speed of a flow in a direction in space not perpendicular to the axis XY.